As shown in FIG. 1, the conventional bicycle shock-absorber 10 is constructed of a cylinder 11 provided with an outer thread 12 on the surface. The outer thread 12 is engaged with a nut 13 and a spring 14. While the upper center rod 15 of the shock-absorber 10 receives a shock and retracts into the cylinder 11, the spring 14 follows in its elasticity to compress. Such structure is defective in design in that the shock-absorber 10 encounters friction forces and is heated as a result thereof. Therefore, the rubber material of the sealed ring in the interior of the cylinder 11 is easily destroyed and deformed by the heat. In addition, the spring 14 is retained by the nut 13 and the nut 13 is easily worsened from its position resulting from expansion and compression of the spring 14. Therefore, the spring 14 of the shock-absorber 10 can not adjust in location.